Procter & Gamble Co. is now spending more than a third of its U.S. marketing budget on digital media, an aggressive shift as Americans for the first time are expected to spend more time online this year than watching television.

P&G chief executive A.G. Lafley said the consumer products giant's digital spending on things like online ads and social media ranges from 25% to 35% of its marketing budget and is currently near the top of that range in the U.S., its biggest market. That is well beyond the estimated 20%...